(How) can I add Multiple Hashtags?

[maidado]

[jeromecc]

Combine them in the search string with OR or AND operators: "#This OR #That" "#This AND #That"

You can build your search string with https://twitter.com/search-advanced (it will be url encoded but you can decode it with an url decoder) and check what is possible there: https://developer.twitter.com/en/docs/tweets/search/api-reference/get-search-tweets